1. Field of the Invention
The present invention relates to orthopedic devices for the stabilization and control of a human knee joint which has been injured. More particularly, the invention relates to a knee brace which will permit the user a relatively high degree of freedom in the use of the bones while, at the same time, permitting control of the joint so as to optimize healing and stability.
2. Description of Related Art
A knee brace of the initially mentioned type is disclosed in one of the present inventor's U.S. Pat. No. 4,890,607. In this patent, a multiaxis controlled motion knee orthosis utilizes a joint mechanism (which is improved over one disclosed in U.S. Pat. No. 4,723,539 of one of the present inventors (Townsend)) having two camming slots and cam pin followers, wherein one camming slot is disposed in a transverse plane and serves to provide the anterior motion of an upper joint piece, while the second camming slot is disposed in a longitudinal orientation and to provide a long arc segment for a unicentric phase of the joint arthrokinematics. During an initial range of motion, pivoting occurs through a short arc segment about an upper cam pin within the longitudinally extending arcuate slot. After the lower cam pin follower reaches the anterior end of the transverse slot, the lower cam pin follower serves as an axis of rotation or pivot point for movement of the upper cam pin follower along the long arc segment of the longitudinal slot.
Such an arrangement provides full control of the forceful action of the joints throughout the entire range of motion while providing a joint of high strength. Furthermore, in knee braces that are custom fit to a particular user, the orthosis of this earlier patent has proved very successful and has been free of significant problems. However, certain shortcomings have been encountered with regard to use of this dual pin and cam slot joint arrangement in less expensive knee braces intended for "off-the-shelf" use. In particular, a generic "off-the-shelf" unit must be fitted by the doctor to a particular user and often involves bending of the femoral and tibial links, such as by bending the femoral links outwardly and the tibial links inwardly to fit someone with larger than average thighs and smaller than average calves.
If such "doctoring" of an "off-the-shelf" unit results in the overlapping surfaces of the joint not being exactly square, these relatively large overlapping surfaces of the links are caused to bind against each other to an extent affecting the performance of the joint. More specifically, this binding produces excessive wearing of the joint, so that the critical tolerances necessary to proper control of the knee can soon be lost. Furthermore, since, during each phase of movement, the motion of the joint is occurring about a single pivot, the full effect of the binding force is concentrated at the single pivot, and is sufficiently great to cause the binding effect to be felt by the wearer to an undesirable degree.
At the other end of the spectrum, in top of the line knee braces, especially for use by professional athletes, the weight of the knee brace is an important consideration, as is high resistance to wear. One way to reduce the weight of the joint, while increasing wear-resistance would be to form the femoral and tibial links of a "space age" lightweight fiber and resin composite material. However, such materials are expensive to machine and are very notch sensitive. Thus, a link having slots as disclosed in the above-mentioned Townsend patents would be cost-prohibitive to produce of a composite material, and would be prone to break apart due to the low notch strength of the composite material.
Thus, it would be desirable and advantageous to produce a joint which would have the benefits of the earlier Townsend designs without their shortcomings. In particular, to have a knee brace with a joint that could be used in inexpensive "off-the-shelf" orthosis without resulting in the wearer feeling a significant binding effect or the joint experiencing excessive wear due to binding. At the same time, such an improved knee brace should possess the capability to be manufactured of lightweight, wear-resistant composite materials.
Four bar linkages are also known for use in knee braces, even for producing polycentric motion. For example, U.S. No. 3,901,223, discloses a knee joint for orthopedic supports and splints using a four bar linkage in which a pair of different length, swinging links pivotally interconnect with bearing points on head portions formed on the ends of femoral (thigh) and tibial (shin) struts. These swinging links and their respective pivot points are designed so that, during flexion of the femoral link relative to the tibial link from a fully extended position of the joint, the longer, forward, link first pivots forwardly through a given angle and then its motion reverses so that the forward link adopts an identical position relative to the tibial link in the fully flexed attitude of the joint (approximately 134.degree. degrees) as it held in the fully extended position. This movement is intended to simulate a movement of the knee in which the locus of the instantaneous centers of rotation approximates a downward and forward curving path, beginning about 3 inches up on the femur and ending at about the position of the femoral epicondyles.
In U.S. Pat. No. 4,821,707 to Audette, a mechanical articulated joint for a knee brace is shown which also uses a four bar type linkage in an attempt to produce a joint which will duplicate the complex motion of the knee; however, at best, the linkage as disclosed in this patent can only do so in a most general way do to the approach taken therein. Furthermore, the design criteria outlined in this patent require that the shape of the condyle be known (which is difficult to do in practice), require use of an arbitrarily set reference line segment and the location of the point of tangency of this arbitrary line segment and the condyle at three positions. As a result, an "off-the-shelf," generic knee brace is virtually impossible to produce in accordance with this patent's teachings, and even achieving of a custom design brace that forces the knee to follow a motion that correctly reproduces the proper complex motion of a healthy knee is problematic.
Thus, there is still a need for controlled motion multiaxis joint for a knee brace which will meet the needs for both "off-the-shelf" and custom top-end knee braces, to an even greater extent than the cam and slot knee orthosis, mentioned above, being less prone to binding problems and being able to be made of composite fiber and resin materials; yet, at the same time, still being able to constrain the tibia to slide rearwardly relative to the femur in an initial range of flexion of the knee from a straight leg position and then to rotate relative thereto along an arcuate path.